The invention disclosed herein relates gamma rays and, in particular, to generating gamma rays from a target material.
Various operations may be performed in a borehole penetrating the earth in the quest for hydrocarbons. The operations can be related to the exploration and production of hydrocarbons. One type of operation is known as well logging.
Well logging is a technique used to perform measurements of an earth formation, which may contain a reservoir of the hydrocarbons, from within the borehole. In well logging, a logging tool, configured to perform a measurement of the earth formation, is conveyed through a borehole penetrating the earth formation. In one embodiment, an armored cable is used to support and convey the logging tool through the borehole. In general, the wireline contains cables for supplying power to the logging tool and communicating data to and from the logging tool.
The logging tool can be configured to perform various types of measurements of the earth formation. Some of the measurements, such as elemental yields and porosity, require irradiating a portion of the earth formation with neutrons. The measurements of the results of interactions between the neutrons and the earth formation can be related to a property of the earth formation, such as the composition or the porosity of the earth formation.
In one logging tool, a chemical source is used to emit the neutrons needed to perform the measurements. Unfortunately, the chemical source can be costly and not readily available. In addition, because the chemical source is radioactive, certain regulatory concerns are associated with transporting and using the chemical source.
In addition, operation of a neutron source may require monitoring of the neutron source during operation. This may require either in-laboratory testing to create baseline values or real-time monitoring of the neutron source in operation.